1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illumination unit of a liquid crystal display device or the like.
2. Description of the Related Art
Liquid crystal display devices are now regularly used as display devices of electronic apparatuses such as personal computers and mobile telephones. Liquid crystal is not a self-luminous display element, and thus an illumination unit for irradiating light onto the liquid crystal panel is required in, for example, a transmissive-type liquid crystal display device. Even in a semitransmissive-type liquid crystal display device that utilizes external light, an auxiliary illumination unit is provided in order to enable the device to be used in dark places. As such an illumination unit for a liquid crystal display device, a spread illuminating apparatus including a light guide plate and a light source disposed to the side of the light guide plate as the main constituent elements is widely used in combination with a liquid crystal display device, because such a spread illuminating apparatus has an advantage in making it thin easily. Further, due to recent enhancements in the performance of white light-emitting diodes (LEDs), spread illuminating apparatuses utilizing white LEDs as a light source are now regularly used in order to achieve further reductions in the size, thickness, and power consumption of spread illuminating apparatuses.
As will be explained later (refer to FIG. 10), such a spread illuminating apparatus includes a light source; a light guide plate that receives light from the light source and emits it, one surface of a pair of opposing principal surfaces of the light guide plate being configured as a light emitting surface; an optical sheet that is disposed on the emitting surface side of the light guide plate and appropriately diffuses light emitted from the light guide plate; and a frame that accommodates these constituent elements.
The thickness of each constituent element has been required to be reduced in order to support the reduced thickness of the spread illuminating apparatus. Due to this requirement, there are cases in which a so-called injection compression molding method is used to mold the light guide plate. In such a method, a light guide plate of a predetermined shape is molded by slightly expanding a cavity of a metallic mold while filling a molten resin therein and then clamping the metallic mold after filling the molten resin so as to narrow the cavity and thereby compress the molten resin.
FIG. 11 illustrates a metallic mold 100 used in the above-described injection compression molding method. The metallic mold 100 includes a fixed mold 102, a movable frame 104 that can separate from/move toward the fixed mold 102 in an opening/closing direction Z of the metallic mold, and a movable mold 106 that can move relatively in the opening/closing direction Z of the metallic mold relative to the movable frame 104. A cavity 108 is constituted by the fixed mold 102 and the movable mold 106. A light guide plate 120 is formed by molding and solidifying a molten resin that has been filled into the cavity 108 into the shape of the cavity 108.
In the structure of the above-described metallic mold, it is necessary to ensure good slidability between the movable frame 104 and the movable mold 106 and to prevent the occurrence of trouble with the metallic mold such as scraping between the movable frame 104 and the movable mold 106 when they are moving relative to each other. Therefore, a slight gap S is provided between the movable frame 104 and the movable mold 106. Further, in the illustrated example, rollers 110 are rotatably disposed in the gap S between the movable frame 104 and the movable mold 106.